Low-water alarm



March 1 1927.

H. B. THURsToN Low WATER ALARM Filed March 19, 1925 r of such an alarmthe dangerously low level the water Patentes Mar. i, i927;

A isiazzz Hartmann, THURs'roNrcLnvnLANn HEIGHTS, o nio.

row-WATER ALARM. 5

i* Application sied March 19,1925. serial No'. 16,627;

This invention relates to lowxwateralarms for steam boilers and the object is to provide an alarm which will be sure of operation while thereis stilla safe amount of water over 'the crown sheet. VThe alarm hereinshown is lof the type wherein a conduit con-v nection is made betweenthesteam space of thej'boiler andan alarm device located eX- teriorly of,tlie'bo'iler, the conduit being normally closed by afusible plugconnected by heat conductingfmeanswith a portion of the fire boX andlocated at the point where the water in the boiler is said to be at adan'- gerous level. lt is desirable to place such a plug within a shortydistance of the uppermost portionv of the crown vsheet of the boiler sothat when the water level reaches and `)asses the region of the plug,the steam above the water level ywill not have sufficient cooling.effect on the metal surrounding the plugto prevent the heat conductedfrom the fire box from melting the plug and opening the passage to thesignal, However, I have found that in the use water may reach a whiletheposition of the boiler is substantially horizontal and thenforinstance, lby reason'of the sudden stopping of a locomotive carryingthe boiler or of such a 4locomotive reaching the end of a level stretchof track and starting down hill the water level ymay fall so far belowthe crown sheet that, although the alarm does sound, the the crownweakened will make is unable Vto withstand the boiler pressure. Anaccident resulting from such a condition would result in serious damageto the boiler and would very likely endanger the lives ofthe crew.

An obvious remedy for this would seem to be to `elevate the positionofthe fusible sheetibefore vthe sheet has become plug so that it wouldrespond in time before ylevel has reached the crown sheet but have foundby extensive and repeated experiments that the likelihood of the fusiblelug, such, as heretofore used, being fused at the rightt-ime Visdiminished by reason of the distance which the heat from the lire boxwill havewto travelto the plug, if it be too remote from the crownsheet.

The-water in 'contact with the alarm cage draws heat away from the meansconducting heat from their@ box to the fusible plug,

water cannot be raised to cover n by overheating'to a degree which and'it freduently happens that the level of i the water may be ywell belowthe crown sheet before the fusible plug melts causing the alarm tosound. is a result of these con` ditions. determined. by experiments, lhave ldevised a means for preventing water slightly above the level ofthe crown sheet, from nullifying the effect Vof the heat passage fromthe-lire box tothe fusible plug, thereby both controlling and moreaccurately gov-` erning the time which the fusible plug will melt'withrelation to the water level above the crown sheet. The means includes aclosedinsulating Jacket surrounding certain of the parts of the alarmassociated with the fusible plugand arranged to insulate the heatconducting path from the fire box to the plug. lt is to' be understoodthat my insulating scheme is intended for use with any type of alarmlocated withinjthe boiler and employing a thermo-responsive 'elementadaptedto act by reason of heat conducted from the lire spacek to soundan alarm.

The details and operation of myinvention will become more clear inconnection with the description to follow which relates to theaccompanying drawings, The essential novel characteristics will besummarized in the claims.

`In the` drawings Fig. lis Va substantially central longitudinal sectionthrough a portion of the low water alarmvembodying the preferred formofy my invention showing the alarm attached to the roof and crown sheetof aboiler; Fig. 2 is a transverse sec-V tion as indicated by the line2-2 on'Fig. l. Indicating 'the various parts of the apparatusbynumerals, l designates a portion of the roof sheet of a boiler, 2 asimilar section of the crown sheet. Access for the live steam to thealarm may include ay combination packing fixture and casing member 5 inthreaded engagement with the roof sheet at 6. The casing has a chamber 7open at the bottom `at 8 through which opening a tube 9 may extendinto'tlie chamber. The tubevinay be spaced apart from the'sides of theopening and is shown as arranged to be separated from the'upper end ofthe chamber whereby a continuous passage may be had from the steam spaceopening Sinto the top of the tube.l y

The tube communicatesat its lowerV end with a plug cage 15 which inthe-type of alarm shown houses the thermo-responsive 'suitable forniadapted to contain a slug,r of

fusible material such as tin alloy shown at 22 filling the upperportuiin `of a longitudinal opening' i213 through the plug. The

upper end of the opening,r is shown as entering a second chamber 24; inthe cage, into which extends a pipe The pipe may ex tend through thetube 9, packing 27, a pack ing glandQ-S and nut 2U, to a signal devicesuch as a whistle 3() located exteriorly of the boiler. The whistleshown inthe drawings `as supported partly by the pipe and partly `by asupporting `eye and bracket 32 and 33 respectively.

The lower end of the casing 15 is shown as closed by the plugr 35threaded at 36 in the casing and as provided with an extension 37projecting dmvnwardly into the fire box. The portion 37 is preferablyprovided with angular surfaces to facilitate its removal from the cage.1

The advantages of such an arrangement of the parts of the alarm are setforth in my prior applications of which an `example is Serial No.726,711 filed July 1S, 1924.

The means whereby I insure the timely operation of the alarm constitutesthe primary feature of my invention. This means is preferably a heat.insulatingr device consistinr of a cvlindrieal casing;r l() shown assurroundingr the cage and extending,r over the adjacent enlarged portionof the tube il. rl"he ends of the casingr may curve inwardly as shown atall land @t2 to engage the wall of said cage and said tube respectively,to forni an insulating;` space between the water chamber and the canje15. Any suitable means may he utilized jl'or holding,Y this insulating,rcasingr in place, such as welding, brazingor the like, about its upperand lower rims at the lines of engagement with the cage 15 and the tubei) as indicated at 4.6 and 17. i

l have found that the distance between the fusible plugr and the crownsheet should be such `that the plug will not melt when there `is stillwater enough in the boiler to permit the safe operation of thelocomotive. Likelihood of the premature fusing `ofthe plug is preventedif the distance is substantially that indicated ,by the proportion shownin the drawings, yet the warning will be given in snicient-time to allowthe o )erator to recover the water `level before` damage has resulted tothe crown sheet.

As previously pointed out, without such a i f i i 1,619,222

below the plug and` perhaps the crown sheet is exposed before the heatmelts the :fusible plug. ,i

` lily the use of inysinvention liowever,l1eat begins to acelnnulate`from the `lire box in the plur 3T and `the surrounding cagegl as soonlas the `general, level ofthe water `slightly `below thetop of the casing40 by which the water is `prevented freni hav-` ing; any direct`cooling,r effect on the cage. l`lierefore by the time the water hasdropped to `about the ,level `even with "the fusible plug 22, thisaccumulated,heat will be sailicient to `melt the plug, .Then the passagewhich includes the chamber `5,`the conduit 9 and the pipe will be openedand the steam will force the now melted particles of the plug outwardalong the pipe 25 ,and sound the alarm.

lt is to be understood that variations in the general design may be madewithout departing from the spirit ofmy invention. .lt will be seen that1` have provided a low water alarm which will1 function to open thepassage and allow `the `alarm to operate at the desired time7irrespective of surging of the water in the boiler and in plenty of timeto )revent any damage `to the crown sheet, and consequent danger tothelives of persons in the vicinity of the boiler.

ll'aving thus deseril'ied my invention, I claim: y

`Ina low water alarm, a member havingnr af passage adapted tocommunicate with the steani space at oneend and with an alarm device atthe other, plug 'arrying` means within the boiler and located adjacentthe crown sheet, and a fusible ,plug carried by said means and normallyinterrupting said passage, means whereby heat conducted from thelrcspace to saidlphuil and an insulating means surroundii'ig a portion ofthe plug cariyini;r means and arranged. to prevent water contact withsaid plug carrying means. y Q. The coinbiinttion with a boiler struotureincludinga .lire box and arcrown sheet, of a low water alarm, said alarmco1npris ing a sin-nal, a member 11i-wine; a plurality of passagesadapted to lead .steam from the boiler tothe signal, a `tusible plug`normally closingr connnunication between said passages, metallic meanssecured to` the crown sheet havinga portion thereof exposed to the heatofthe `fire box for conducting heat therefrom to the plug, a jacketsurrounding said means for preventing water contacting with the heatconducting means, the jacket lll) preventing contact from a pointadjacent the crown sheet to a point materially above the fusible plug.

3. The combination with a boiler structure including a fire box and acrown sheet, of a ,low water alarm, said alarm comprising a signal, amemberv having a pluralityr vto melt the pluO'.

et. The combination with a boiler structure including a fire box and acrown sheet, of a low water alarm, said alarm comprising a signal, amember having a plurality of passages adapted to lead steam from theboiler to the signal, a fusible plug normally closing communicationbetween said passages, heat conducting means extending be tweenv thecrown sheet of the boiler and the plug and an insulating jacketsurrounding a portion of said heat conducting means in the zone of theplug, whereby when the water in the boiler drops below the top of theacket, heat conducted from the fire space accumulates rapidly in theregion of the plug lcausing it to be fused.

5c. A low water alarm for a boiler having a roof sheet and a crownsheet, the alarm comprising in combination a signal, a member having apassage leading from within the boiler to the signal, a fusible plugnormallyV closing said passage, means secured to the crown sheet forcarrying said plug, having a heat conducting portion extending withinthe fire box for leading heattherefrom to the plug, a surroundinginsulating jacket for preventing Contact of the water in the boiler withsaid conducting means said jacket extending from a point nearthe crownsheet to a point above the plug, ywhereby when the meanl level of thereceding water in the boiler reaches the last named point, the water isprevented from withdrawing heat from the conducting member. l A

6. A low water alarm comprising a casing member adapted to be secured tothe roof sheet of a boiler, a member having a passage communicating withthe casing for conducting steam therefrom, means normally closing thepassage including a fusible metallic plug, a plug cage supporting saidclosingl means having a portion thereof in communication with thetirespaceof the boiler, a Vpassage leadmg from the plug to the exterior ofthe boiler adapted to communicatev with'a signal device and a heatinsulating casing spaced apart from the plug cage the zone of the plugand contacting therewith above and below the zone' of the plug wherebywater in the boiler is maintained out of contact with the cage at thispoint.

7. The combination with a boiler structure including a lire box and acrown sheet, of a low water alarm, said alarm comprising a signal, amember having a plurality ofpassages adapted to lead steam from theboiler to the signal, a fusible plug nor-- mally'closing communicationbetween said passages, means in threaded engagement with the crownsheetfforming a part of said passages and carrying said fusible plug,means within and in threaded engagement with said last named means forconducting heat from the re box to the plug and an insulating meanscomprising a jacket substantially preventing water contact with the plugmounting and said conducting means.

8. The combination with' a boiler structure including a fire box and acrown sheet, of a low water alarm, said alarm comprisingpa signal, amember having a plurality of passages adapted to lead steam from theboiler to the fsignal, a fusible plug norvmally closing communicationbetween said passages, means carried by the crown sheet and Vforming apart of said passages for carrying said fusible plug, means within saidlast named means for conducting heat from the lire box tothe plug and aninsulating means surrounding the last two mentionedmeans comprising awater tight jacket separated from the plug carrying means in the Zone ofthe plug and contacting therewith above and below this Zone.

9. In a low water alarm, a metallic container located within a boilerand secured to the crown sheet thereof, a. thermo-responsive element'carried thereby, means affording heat conductivity from the fire spaceof the boiler to the container, an alarm externally of the boilerarranged to be actuated under the control of said element, andinsulating means in spaced relation to the containerv and embracing thesame, for preventing wat-.er contact with the embraced portion of thecontainer. Y

l0. In a low water alarm, a container located within a boiler, athermo-responsive element supported thereby, means extending into thefire space and in threaded engagement with the container above the crownsheet of the boiler for providing direct heat conductivity from the firespace to the element, an alarm externallyof the boiler ar- Y ranged ytobe actuated consequent upon the fusing of the element, and insulatingmeans in spaced relation tothe container, surl rounding the same andsealed against Athe entranceV of fluid in the boiler whereby such liuidis prevented from container. 1

1.1, ln low veterani-111, a hollow Concontacting with the Y tainermember located Within the steam and Water chamber of a boiler, athermo-responsive element supported thereby, a Signal de vice locatedexternally of the boiler and arranged to be actuated under control ofsaid element, a closure member tor the container extending into the tirespace ot the boiler and beingr in intimate contact with the containerabove the crown sheet ot the boiler forproviding direct heatcomlactivity to the element tromthe tire space, and an insulating meanscomprising a jacketembracing,r a portion of the first named member andthe said element,the jacket being sealed about the hollow `member toprevent the steam and Water from contacting with the embraced portion.

1Q. In a low Water alarm, a hollow con tainer located Within a boiler, athermo-responsive element carried by the container and removable`therefrom from Within the tire box ot the boiler, means including aclosure member for the container in spaced relation to theV crown sheetand extending; therethrough tor conducting llcat `freni tbc fire spacetothe element, an alarm device externally ofthe boiler arranged to beactuated consequent upon snllicient heating ot the element, andinsulating' means surrounding and spaced apart itrom the container tor adistance along the Same.

13. In a low water alarm for a boiler, a cage `located within theboiler7 a thermoresponsive element within the cage and located entirelyabove the crown sheet oit the boiler, an alarmV externally oil theboiler arranged to be actuated under control of the element and a`jacket surrounding and .epaced apart from the cage and secured theretoin enveloping relation itor preventing,f direct contact ot Water orsteam in the lmilcr with the caee.`

l-l. In a low Water alarm :for a boiler, a cage Within the boiler, athermo-reeponSive element Within the cage, an alarm external-` ot theboiler arranged to be actuated Under control of the Said element and atubular insulating jacket embracing the cane, .epaced apart therefromintermediately of its ends and in sealed relation thereto at its ends.

In tetimony whereof, I hereunto aflix my signature.

HERMAN B. THURSTON.

